U.S. Immigration and Customs Enforcement agents blitzed dozens of 7-Eleven stores before dawn Wednesday to interview employees and deliver audit notifications, carrying out what the agency said was the largest operation targeting an employer since President Trump took office.

ICE said its agents showed up at 98 stores and made 21 arrests, describing the operation as a warning to other companies that may have unauthorized workers on their payroll.

"Today's actions send a strong message to U.S. businesses that hire and employ an illegal workforce: ICE will enforce the law, and if you are found to be breaking the law, you will be held accountable," said Thomas D. Homan, the agency's top official, in a statement.

Homan characterized the operation as a new front in the Trump administration's broader immigration crackdown and its effort to increase deportations. ICE agents have made 40 percent more arrests in the past year.

"Businesses that hire illegal workers are a pull factor for illegal immigration and we are working hard to remove this magnet," Homan's statement said. "ICE will continue its efforts to protect jobs for American workers by eliminating unfair competitive advantages for companies that exploit illegal immigration."

ICE said it sent agents to deliver audit notifications and conduct interviews at 6 a.m., temporarily shutting down ­7-Eleven stores in the District and in 17 states: California, Colorado, Delaware, Florida, Illinois, Indiana, Maryland, Michigan, Missouri, Nevada, New Jersey, New York, North Carolina, Oregon, Pennsylvania, Texas and Washington.

Irving, Tex.-based 7-Eleven has more than 60,000 stores worldwide, according to its website. In a statement, the company said it was not responsible for the hiring decisions of individual franchise owners.

"7-Eleven Franchisees are independent business owners and are solely responsible for their employees including deciding who to hire and verifying their eligibility to work in the United States," the company said in an emailed statement.

"As part of the 7-Eleven franchise agreement, 7-Eleven requires all franchise business owners to comply with all federal, state and local employment laws," the statement continued. "7-Eleven takes compliance with immigration laws seriously and has terminated the franchise agreements of franchisees convicted of violating these laws."

ICE described Wednesday's sweep as a follow-up enforcement operation that built on a 2013 raid resulting in the arrests of nine 7-Eleven franchise owners and managers. They were charged with "conspiring to commit wire fraud, stealing identities and concealing and harboring illegal aliens employed at their stores," according to the agency.

ICE said all but one pleaded guilty and were ordered to pay more than $2.6 million in back wages to workers.

Last year, ICE said it conducted 1,360 employee audits, making more than 300 arrests on criminal and administrative violations. Businesses were ordered to pay $97.6 million in judicial forfeiture, fines and restitution, the agency said, and $7.8 million in civil fines.

"We are going to be doing more of this work and dedicating more resources to make sure businesses are complying with the law," said Dani Bennett, an ICE spokeswoman. "This is a demonstration of our commitment to enforcing the law."

Store owners and managers will have three days to provide the agency with information about the immigration status of their employees, Bennett said.

Prosecuting business owners who hire illegal workers is often difficult for the government, because company owners typically insist they were deceived by employees using fake Social Security numbers.

Supporters of tougher immigration enforcement want to require all employers to use the government's E-Verify system, which checks employees' I-9 employment eligibity forms, Social Security numbers and other identifying information with federal databases. Critics say E-Verify is error-prone and a needless expansion of government power.

Nearly 8 in 10 Americans said employers should be required to validate the immigration status of new hires, including 6 in 10 who support it strongly, according to a September 2017 Washington Post-ABC News poll.

Large majorities of Democrats (65 percent) and Republicans (93 percent) said they would back such a mandate, the survey found.

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Nick MiroffNick Miroff covers immigration enforcement, drug trafficking and the Department of Homeland Security on The Washington Post’s National Security desk. He was a Post foreign correspondent in Latin America from 2010 to 2017, and has been a staff writer since 2006. Follow